Japanese Patent Publication JP10-318779 discloses an exercise intensity level storing device which utilizes a body sensor which provides an electric signal indicative of the body motions of the user. In order to determine the exercise intensity, the device includes a processor that converts the body motions into the number of steps taken to give a combination of the amplitude of the electric signal and the number of steps. Then, the processor refers to a relation already obtained between the combination and an exercise intensity scale to obtain therefrom one of the exercise intensities in the scale as corresponding to the combination. Unfortunately, the above scheme is found not satisfactory in giving an accurate exercise intensity truly indicative of the body motions taken by the user.